Your software doesn't like your media. Could be a million different reasons from incompatible video and/or audio formats, medias encode is too complex for the software and/or hardware, etc. Keep in mind the player software still needs to support a format/codec regardless of whether the hardware can natively or not. This 4k 60fps h265 video will play on the ATV4K using Infuse 5. I'm using a NAS with no server/transcoding software to verify all the decoding is being done on the AppleTV via software/hardware.